DSL (Digital Subscriber Line) Rings, such as disclosed in U.S. patent application Ser. No. 11/463,240, filed on Aug. 8, 2006, in U.S. Provisional Patent Application Ser. No. 60/706,022, filed on Aug. 8, 2005, and in International (PCT) Application Serial No. PCT/CA2008/001079, entitled “BONDED INTERCONNECTION OF LOCAL NETWORKS” and filed on Jun. 9, 2008, the entire contents of all of which are incorporated herein by reference, represent new and powerful reconfigurations of existing telecommunication network resources.
Such rings enable higher bandwidths to be achieved at greater distances from a CO (Central Office). As those skilled in the art will appreciate, the transmission bandwidth of technologies such as DSL and Ethernet decreases with distance. In a star network architecture for instance, a DSLAM (DSL Access Multiplexer) is physically located in the middle, but the distance to each subscriber is often greater than the relatively short distance required for maximum bandwidth. DSL Rings greatly increase the distance and bandwidth-carrying capability of the ‘local loop’. High bandwidth is made available to households by reducing the transmission distance to the distance between households instead of the distance between households and COs. Maximum bandwidth can be obtained if the distance between households that are connected together is less than the maximum bandwidth distance.
The high bandwidth capability provided by DSL Rings could be used, for example, to provide network backhaul for bandwidth-intensive end user applications. Wireless network operators and service providers, for instance, are continually striving to provide higher bandwidth to their subscribers. Services such as wireless streaming video could potentially be supported if wireless bandwidth of 100 Mbps were available.
Such high bandwidths cannot be provided in current wireless communication networks that are based on “macrocell” designs. For example, a typical wireless site is serviced by four T1 lines, which can support 112 simultaneous cell phone calls and limited Internet capability. The cost of upgrading the macrocell approach is prohibitive and will not support the necessary coverage with the necessary bandwidth. Alternate network implementations based on other technologies are therefore being explored. Femtocells are representative of one such technology.
A femtocell is a small cellular base station used in residential or small business applications, which connects to a service provider's network and normally supports less than 10 mobile devices. Femtocells allow service providers to effectively extend service coverage indoors or over a relatively short range, where access might otherwise be limited or unavailable. While a femtocell itself might support bandwidths on the order of 100 Mbps, the challenge of providing the 200-300 Mbps bandwidth necessary for backhaul to a main network still remains.
This is one scenario in which the high bandwidth capability of DSL Rings having bonded links back to a main network can be particularly useful. However, proper operation of a femtocell, which might be implemented at each node in a ring for example, requires accurate synchronization (e.g., 50 parts per billion—ppb—or better) with the service provider's network. A femtocell station lacking accurate synchronization will exhibit undesirable behaviour such as call dropping or the inability to establish calls reliably. Traditionally local synchronization was accomplished either with a GPS (Global Positioning System) unit at each node or with a dedicated BITS (Building Integrated Timing Supply) synchronization line to each node, as is the case with SONET/SDH (Synchronous Optical NETwork/Synchronous Digital Hierarchy) optical systems. Where many individual femtocells are deployed, as might be the case in a DSL Rings implementation, the use of a dedicated GPS unit or a local synchronization line for each femtocell becomes cost prohibitive.
Another possible option would be a wireless-based synchronization signal. This approach, however, would take traffic-carrying bandwidth out of the highest revenue part of a communication system. An NTP (Network Timing Protocol) packet-based approach, while possibly being cost effective, might not be sufficiently accurate. Precision Timing Protocol (IEEE 1588) would be accurate and cost effective, but suffers quality degradation as the distance from the timing source increases.
At least some of these issues could also affect synchronization of other communication equipment, such as a traffic processor and/or other elements of a ring node itself, for instance.